Reaction apparatus for the production of industrial gases, such as hydrogen, are well know in the prior art. These fuel processing apparatus employ steam reforming as the most common method for producing hydrogen from hydrocarbon fuels such as natural gas or naphtha. Conventional commercial size fuel processing apparatus (reformers) are typically very large constant output elements that are limited in their ability to adjust to variable demand or flow requirements.
Electric power generating devices known as fuel cell power plants are electrochemical devices that operate by consuming hydrogen on an anode electrode of their fuel cell stack assembly (CSA). The hydrogen demand of the fuel cell power plant is variable and therefore not easily adaptable to the constant output characteristics of conventional commercial size reformers. This led the assignee into the successful development of a compact reformer and its associated technology. The compact reformer, operating as an integral part of the power plant, is characterized by the ability to produce a hydrogen rich stream that varies in response to changing power plant hydrogen consumption. This technology is exemplified in assignee's U.S. Pat. Nos. 4,098,588 and 4,098,589.
It is also recognized that other industrial gas requirements exceed the hydrogen purity levels typically produced by a fuel processing apparatus of either the conventional commercial size designs or the compact reformer designs used in fuel cell power plants. To meet such higher purity hydrogen requirements, additional processing by secondary devices such as pressure swing absorption (PSA), cryogenic or membrane elements can be used. However, when this higher purity requirement is combined with variable demand only a compact reformer of the type used in fuel cell power plants has the inherent ability to meet this need. Unfortunately, it is not possible to directly couple a compact reformer to a secondary unit such as a PSA device without making significant changes in the reformer unit's operational control system.
A fuel cell power plant reformer seeks to supply hydrogen rich gas to the CSA in response to hydrogen consumption which is proportional to the fuel cell gross current or electrical load. The fuel cell power plant exhaust gas (waste gas), depleted in hydrogen, is fed to the reformer burner to provide heat for the steam reforming process. Reformer process fuel and steam feed is adjusted in proportion to the fuel cell gross current, but with the requirement to also maintain a set reformer temperature.
For a fuel cell power plant operating at a steady point, constant hydrogen consumption, the reformer temperature can be increased by increasing the reformer fuel feed because it results in a direct and rapid increase of the amount of exhaust gas fed to the reformer burner. This means added energy input to the reformer and hence a rise in reformer temperature. Conversely, a reduction in fuel feed at any steady operating point means a drop in reformer temperature.
This direct link between reformer fuel feed and reformer heating in a fuel cell power plant is not possible when a compact reformer is connected in series to another hydrogen consumption or extraction process such as a PSA unit. The PSA waste gas or blow down purge gas is used by the reformer burner to heat the unit. However, the flow rate and heating value of this waste gas depends on the specific operation of the PSA unit, but there is no direct link between the fuel feed level to the reformer and the quality or quantity of waste gas supplied back to the reformer burner.
There exists a need, therefore, for a system and method of gas generation, and a temperature and flow control system and method therefor, which accounts for the lack of a direct link between feed gas and the waste gas fed to reformer burners thereof from a down stream unit such as a PSA, and which is applicable to multiple reformers joined together as a single operating unit to provide increased capacity, wherein each unit requires its own waste gas supply from the PSA and individual control of its temperature.